Knife sharpener



FIG. 1 illustrates a right side elevational view of a knife sharpenerembodying my design, the left side being a mirror image thereof;

FIG. 2 demonstrates a front end view of the design as shown in FIG. 1,the rear end view being identical thereto;

FIG. 3 shows a top plan view of the design as shown in FIG. 1; and,

FIG. 4 shows a bottom plan view thereof.

The ornamental design for a knife sharpener, as shown and described.